The present invention relates generally to molding optical lenses, more particularly, although not necessarily exclusively, ophthalmic lenses, i.e. spectacle lenses, in particular when the corresponding molding material is a synthetic material that can be polymerized by irradiation.
As is known in the art, two molding shells are usually employed to mold an optical lens and adapted to define between them, in conjunction with a closure member operative at their periphery, the necessary molding cavity, and the latter is filled with molding material.
At present, in mass production, some or all of the corresponding operations are usually carried out manually.
However, nowadays, to meet the expectations of interested parties, who wish to take delivery as quickly as possible, and nevertheless to satisfy a large number of envisagable prescriptions, which can be highly varied, there is a requirement for unitary production.
As a corollary to this it is desirable for at least some of the diverse operations required to be fully or partly automated.
In this instance, the particular problem is that, to satisfy any particular prescription, it is necessary to ensure rigorous control of the position of the two molding shells relative to each other.
In the case of prescriptions requiring a torus, for example, the torus of the molded optical lens depends on the angular position of the two molding shells relative to each other, independently of the thickness at the center, which depends on the corresponding distance at the center between two molding shells, and the prism of the lens depends on any inclination of one or both of the molding shells relative to any transverse plane taken as a reference plane.
The present invention provides a method and an installation for surmounting these difficulties and in particular authorizing very fast fabrication of any ophthalmic lens responding to a given prescription, as soon as an order is received, and preferably in less than one hour.
The method according to the invention is generally characterized by the execution of the following operations: each of the two molding shells is placed in one of two respective individual holding means adapted to rotate about a common centering axis, if necessary, at least one of these holding means is turned about that centering axis, until the angular position is reached corresponding to the required torus, if any, each of the two molding shells is extracted from its holding means with the aid of picking means, the inclination, if any, of each of the molding shells with respect to a reference plane is checked with the molding shell engaged in this way with its picking means, if necessary, until the inclination corresponding to the required prism is reached, the position of at least one of the molding shells on its picking means is adjusted, the two molding shells are moved one toward the other with the aid of their picking means, preserving their position with respect to this picking means, the closure member is placed around the two molding shells, and the molding cavity formed in this way is filled with molding material.
If the molding material is a synthetic material that can be polymerized by irradiation, the combination consisting of two molding shells, the closure member and the mass of molding material filling the corresponding molding cavity is then exposed to irradiation means.
As a corollary of this, and ignoring any initial placing of each of the molding shells in holding means, the installation according to the invention includes the means for automatically executing the above various operations.
To be more precise, it includes, in addition to the necessary two holding means and two picking means, at least two separate workstations for executing the required operations and transfer means for relative movement of each molding shell with respect to each workstation.
The two molding shells are preferably treated at the same time.
To control their inclination, if any, relative to a reference plane, and therefore to obtain any required prism, the front face, and thus the active face, of each molding shell, i.e. its face which defines the molding cavity, is preferably pressed against feelers for assessing the distance of a chosen number of points on that active face relative to the reference plane adopted.
The use of such feelers is undoubtedly disclosed in French patent No. 1 316 497.
However, in French patent No. 1 316 497 the feelers are operative on the rear face of the molding shells, and thus on the opposite face of the molding shells to the molding cavity, and the molding shells are brought into contact with the feelers by injecting compressed air between them.
Under these conditions, it is not possible to ensure that the molding shells are not subjected to any unintentional movement, to the detriment of their relative position with respect to each other, when the compressed air supply is disconnected.
This does not apply when, in accordance with the invention, the feelers are operative directly on the active face of the molding shells, while each is being held correctly by its picking means.
As a corollary of this, the various transfer means operative from one workstation to another in the molding installation according to the invention advantageously guarantee conservation of the centering axis common to the two molding shells.